Portable handheld work apparatus, which are driven by an internal combustion engine, have a radial fan for cooling the engine in known embodiments. These work apparatus include chain saws, brushcutters, suction/blower apparatus or the like. The radial fan includes a fan wheel and a spirally-shaped fan housing at least partially enclosing the fan wheel. The fan wheel is assembled on the crankshaft of the engine and rotates at the same rpm. The fan wheel can also be used for controlling an ignition system of the engine by utilizing the rotation of the fan wheel which is in synchronism with the crankshaft. For this purpose, an ignition coil and an ignition magnet, which rotates with the fan wheel, are so arranged with respect to each other that an ignition in the engine is caused by the ignition magnet running by the ignition coil at a preadjusted time point. The ignition magnet is fixed on the fan wheel and the ignition coil projects into the interior space of the fan housing.
Embodiments of a fan arrangement of such work apparatus are known wherein a take-out opening is provided in the radial fan in the region of the moved air flow. The take-out opening diverts a combustion air flow for the internal combustion engine branched out from the air flow. A backup pressure is caused by the high speed of the cooling air flow and, by utilizing this backup pressure, the branched-off combustion air flow is fed at an overpressure through a combustion air channel to the carburetor of the engine.
During operation of a portable handheld work apparatus under corresponding ambient conditions, dust particles or the like can be drawn in by suction by the cooling fan wheel which are entrained and moved within the cooling fan together with the air flow to be moved. Various embodiments of so-called preseparators are known by means of which the particles entrained in the air flow are intended to be held away from the take-out opening for the combustion air flow. The effect of such preseparators is dependent upon the position and the flow conditions and is therefore not always satisfactory. The dirt particles, which are conducted away through the take-out opening and are supplied together with the combustion air flow to the carburetor, can lead to an unwanted high load on an air filter mounted forward of the carburetor. As a consequence, frequent exchanges of filters result and reduce the efficiency of such work apparatus. The arrangement of take-out opening and preseparators in the fan unit can also lead to a disadvantageous influencing of the moved cooling air flow and therefore the targeted cooling capacity. Furthermore, the achievable pressure gain in the combustion air flow is not always satisfactory.